Field
Embodiments of the present invention generally relate to a method and apparatus for plasma etching substrates and, more specifically, to a method and apparatus with protection for edges, sides and backs of the substrates being processed.
Description of the Related Art
During photolithography, a substrate, such as a photomask, or “reticle,” is usually positioned between a light source and a wafer being processed to form patterned features on the wafer. The substrate contains a pattern reflecting configuration of features to be formed on the wafer.
A photomask substrate typically includes a substrate of an optically transparent silicon based material, such as quartz, having a light-shielding metal layer metal, typically chromium, formed on a working surface and a highly reflecting coating, such as chromium nitride, formed on the rest of the surfaces. The light-shielding metal layer is patterned and etched to form features which define the pattern, which corresponds to the features to be transferred by a photolithography process to wafers, such as semiconductor wafers.
Deposition and etching processes are usually employed to fabricate the patterned photomask substrates. The highly reflective coating can be damaged during deposition or etching processes. For example, while using a plasma to etch the pattern in the light shielding metal layer, the highly reflective coating can be degraded if exposed to the plasma. FIG. 1 is a schematic side view of a substrate 100 being processed in a plasma environment. The substrate 100 includes a substrate 102 having a light-shielding metal layer 104 formed on a top surface 112 and a light reflecting coating 106 formed on a bottom surface 114 and side surfaces 116. Traditionally, while forming a pattern on the light-shielding metal layer 104, the substrate 100 is disposed on a supporting assembly 108 with the light-shielding metal layer 104 facing a plasma 110. However, the light reflecting coating 106, particularly the light reflecting coating 106 on the side surfaces 116, may be exposed to the plasma 110 thus being compromised during the process.
Therefore, there is a need for a method and apparatus forming patterns on a substrate without damaging the reflecting coating on the substrate.